Modular knee joint prosthesis

ABSTRACT

A knee joint prosthesis includes a femoral component for engaging the femur having an articular surface and a recess within the articular surface, and a tibial component for engaging the tibia with a bore, and a meniscal component comprising a rotation pin configured for rotatable mounting within the bore of the tibial component. The meniscal component also includes a bearing surface for sliding contact with the articular surface of the femoral component and an elongated channel defined amid the bearing surface. A stabilizing post is provided that includes a base slidably mounted with the elongated channel and a spine post projecting from the base through the channel and into the recess when the articular surface is in contact with said bearing surface. The stabilizing post thus slides within the channel when contacted by the interior of the recess in the femoral component. In a method of the invention, a plurality of stabilizing posts can be provided for temporary mounting within the channel. A stabilizing post can be selected that provides an optimum joint movement.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to prosthetic joints, andparticularly to a prosthesis for the knee joint.

[0002] Implantable knee prostheses for diseased and/or damaged kneestypically include three components, namely a femoral component, a tibialcomponent and a meniscal component. The femoral component may alsoinclude a patellar element, or a separate patellar component may beprovided. The prosthesis components are generally configured to restoreor emulate as much of the natural motion of the knee joint as possible.The selection of the particular prosthesis components is usuallydictated by the condition of the patient's knee. For instance, thecondition of the distal end of the femur and proximal end of the tibia,as well as the patency of the surrounding ligaments and soft tissue canaffect the form of the joint prosthesis.

[0003] Generally, a total knee joint replacement includes a tibialcomponent having a platform portion which replaces the entire superiorsurface of the tibial plateau and substitutes for the tibial condylarsurfaces. The femoral component also includes laterally-spaced condylarportions joined by an intercondylar bridge and a patellar surface.

[0004] The tibial component typically includes a tibial tray and stemfor surgical attachment to the proximal end of the tibia. The componentalso includes an intermediate articulating surface member that isconnected to the tibial tray. The intermediate member defines a bearingsurface for articulation of the femoral component thereon. The matingsurfaces are smoothly curved in the anterior-posterior (AP) direction togenerally match the lateral profile of the natural femoral and tibialcondyles, and to ultimately replicate the normal joint movement.

[0005] This normal joint movement includes a translational component inthe AP direction, as well as a rolling of the femoral condyles on thetibial condyles when the knee is flexed. In addition, the natural tibiais capable of rotation relative to the femur about the axis of thetibia. Thus, an ideal knee prosthesis will be able to achieve all threedegrees of freedom of movement. In some cases, the patient's knee lacksadequate posterior support due to a deficient posterior cruciateligament. In these cases, the modular knee is preferably posteriorlystabilized, meaning that posterior movement of the tibia relative to thefemur is restricted. This posterior stabilization can be achieved in atypical implant by a projection or eminence on the tibial insert thatengages a box-like intercondylar portion of the femoral component.Intact collateral ligaments keep the projection within the box-likeportion as the knee is flexed to inhibit dislocation of the joint athyper-extension or hyper-flexion.

[0006] In order to increase the lifetime of the prosthetic knee joint,the mating bearing surfaces between the tibial and femoral componentsgenerally permit a combination of rolling and translational movement asthe knee joint is flexed. These two degrees of freedom of movementchange the direction of forces between the two components so the forcetransmitted through the joint is not focused on one location. Inresponse to this optimum design aspect, some prosthetic knees include atranslating intermediate bearing component. One problem with modularimplants of this type is that the articulating and sliding componentscan be exposed to the soft tissue surrounding the joint.

SUMMARY OF THE INVENTION

[0007] In one embodiment of the invention, a modular joint prosthesiscomprises a first joint component having a bone engaging portion, anarticular surface, and a recess defined within the articular surface.The prosthesis further includes a mating component having a boneengaging portion and defining a bearing surface for sliding contact withthe articular surface of the first joint component. In one feature ofthe invention, a stabilizing post is slidably mounted to the matingcomponent amid the bearing surface with the post projecting from themating component and into the recess when the articular surface is incontact with the bearing surface.

[0008] In certain embodiments, the mating component includes a secondjoint component including the bone engaging portion and an intermediatecomponent connected to the second joint component, the intermediatecomponent including the bearing surface. When the modular jointprosthesis is a total knee prosthesis, the first component is thefemoral component, the second component is the tibial component and theintermediate is the meniscal component.

[0009] The second joint component can define a bore, while theintermediate component can includes a pin sized to be received withinthe bore. The bore and pin can be configured to permit relative rotationtherebetween when the pin is received within the bore to add arotational degree of freedom between the femoral and tibial components.

[0010] In one aspect of the invention, the mating component or theintermediate component defines an elongated channel. The stabilizingpost includes a base configured for sliding engagement within thechannel and a spine projecting from the base through the channel andinto the recess when the articular surface is in contact with thebearing surface. In certain embodiments, the channel is open at one end.In these embodiments, a locking member can be provided that isconfigured to close the one end with the base of the stabilizing postdisposed within the channel. The locking member can be configured for apress-fit within the channel.

[0011] In some embodiments, the channel includes an enlarged groove atopposite sides of the channel. The base of the stabilizing post can thenbe configured for sliding engagement within the grooves, while thelocking component can be configured for locking engagement within thegrooves. Preferably, the channel has a length greater than the length ofthe base so that the base can translate within the channel.

[0012] The recess of the first joint component can define surfaces atits opposite ends. The stabilizing post preferably includes a faceopposing each of the opposite end surfaces. The recess surfaces and acorresponding opposing face of the stabilizing post are configured toprovide a camming movement of the stabilizing post as the recess endsurface moves in contact with the opposing face. Thus, as the firstjoint component rolls and translates relative to the mating component,the camming movement causes the stabilizing post to slide between theends of the channel.

[0013] In some embodiments, two faces of the stabilizing post aredifferently curved to provide different camming effects at opposite endsof the channel. In one feature of these embodiments, a plurality ofstabilizing posts can be provided having different profiles. Anappropriate stabilizing post can be selected during a total kneeprocedure to optimize the movement of the resulting prosthetic joint.

[0014] It is one object of the present invention to provide a prostheticjoint that permits relative rolling and translation between two boneengaging components. A further object is achieved by features of theinvention that reduce the exposure of articulating surfaces andcomponents of the prosthetic joint to soft tissue surrounding the joint.

[0015] These objects and certain benefits of the invention can beascertained from the following written description taken together withthe accompanying figures.

DESCRIPTION OF THE FIGURES

[0016]FIG. 1 is an exploded perspective view of the components of ajoint prosthesis in accordance with one embodiment of the invention.

[0017]FIG. 2 is a side exploded view of the intermediate component ofthe joint prosthesis shown in FIG. 1.

[0018]FIG. 3 is a top elevational view of the intermediate componentshown in FIG. 2.

[0019]FIG. 4 is an end elevational view of the intermediate componentshown in FIG. 2.

[0020]FIG. 5 is a side elevational view of the intermediate componentshown in FIG. 2, with the stabilizing post shown in different positions.

[0021]FIG. 6 is a side elevational view of the femoral component of theprosthetic joint shown in FIG. 1.

[0022]FIG. 7 is a side elevational view showing one position of thefemoral component relative to the intermediate component of theprosthetic joint shown in FIG. 1.

[0023]FIG. 8 is a side elevational view showing another position of thefemoral component relative to the intermediate component of theprosthetic joint shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] For the purposes of promoting an understanding of the principlesof the invention, reference will now be made to the embodimentsillustrated in the drawings and described in the following writtenspecification. It is understood that no limitation to the scope of theinvention is thereby intended. It is further understood that the presentinvention includes any alterations and modifications to the illustratedembodiments and includes further applications of the principles of theinvention as would normally occur to one skilled in the art to whichthis invention pertains.

[0025] Referring first to FIG. 1, a modular joint prosthesis 10 isdepicted that comprises a first joint component 12, a second jointcomponent 14 and an intermediate joint component 16. From theperspective of a knee prosthesis, the first joint component 12 can bereferred to as the femoral component, the second joint component 14 asthe tibial component, and the intermediate joint component 16 as themeniscal component.

[0026] The femoral and tibial components can be configured according toknown designs for these elements. For the purposes of the presentdisclosure, certain details of these components will be described. Thefemoral component 12 can include an articular surface, or moreparticularly a pair of condylar articular surfaces 25. These surfacesare smoothly curved and configured to emulate the shape of the naturalfemoral condyles. The component 12 also includes a bone engaging portion27 which can include fixation posts 28. The bone engaging portion 27 canbe configured in a known manner for attachment to the distal femur. Thefemur can be prepared in a conventional manner to accept the femoralcomponent 12.

[0027] The femoral component 12 can further include a patellar element30 that is integral with the articular surfaces 25. A separate patellarelement can also be provided for connection to the femoral component.The component 12 also includes an intercondylar recess 32 which ispreferably a box-like structure spanning the AP dimension of thecomponent. A slot 33 can be included in the proximal face of the recess32. In one feature of the femoral component 12 of the presentembodiment, a tab 34 can be provided at the posterior end of the recess32. The tab 34 can operate as a control for roll-back of the tibiarelative to the femur as the joint is articulated.

[0028] The tibial component 14 can be in the form of a conventionaltibial tray. The component includes a proximal surface 35 that parallelsthe tibial plateau cut into the proximal end of the tibia to receive thecomponent. A fixation stem 37 projects downwardly from the tibial trayand is configured for solid, permanent fixation within the prepared endof the tibia. A connection bore 39 extends from the proximal surface 35into the fixation stem 37. The bore is configured to receive a matingstem 45 of the intermediate joint component 16 in a known fashion. Toapproximate the shape of the prepared end of the tibia, the tibialcomponent 14 can define a posterior recess 41.

[0029] Turning now to the intermediate component 16, details of itsdesign can be gleaned from FIGS. 1-4. In general, the intermediatecomponent can be configured like similar components from known modularknee prostheses. Thus, the intermediate component 16 can includeopposite spaced-apart bearing surfaces 43 that are configured forarticulating contact with the articular surfaces 25 of the femoralcomponent 12. The component 16 can also include a rotation pin 45 thatis rotatably mounted within the connection bore 39 of the tibialcomponent 14. The interface between the rotation pin and the tibialcomponent bore can be of conventional design that permits relativerotation between the intermediate component 16 and the patient's tibia.In the illustrated embodiment, the axis of rotation of the intermediatecomponent 16 is at the center of the component and of the tibialcomponent 14; however, other axes of rotation are contemplated asrequired for the particular joint anatomy and the desired movement ofthe joint prosthesis.

[0030] In a modification from prior intermediate components, thecomponent 16 of the present invention includes a channel 47 definedbetween the spaced-apart bearing surfaces 43. In general, the positionof the channel 47 corresponds to the position of the recess 32 of thefemoral component 12 when the two components 12 and 16 are inarticulating contact. The channel 47 can include a posterior opening 49at the posterior side of the intermediate component 16. A stop surface51 is provided at the closed anterior end of the channel 47. Oppositegrooves 53 can be formed at the base of the channel 47 for reasons setforth below. As shown in the figures, the channel 47 extendssubstantially along the entire AP length of the intermediate jointcomponent 16.

[0031] The channel 47 is configured to receive a further novel componentof the prosthesis 10, namely the stabilizing post 18. The stabilizingpost 18 projects upward from the intermediate component 16 to engage theintercondylar recess 32 in the femoral component 12. As best illustratedin FIGS. 1 and 2, the stabilizing post 18 includes a base 55 that issized for sliding engagement within the grooves 53 of the channel 47.The base 55 and grooves 53 preferably form a close running fit so thatthe stabilizing post 18 can slide freely within the channel 47 withoutbinding.

[0032] The stabilizing post 18 includes a spine 57 that projects fromthe base 55. The spine 57 is sized for sliding movement along theexposed length of the channel 47 facing the femoral component recess 32.The spine 57 has a height from the base 55 that is sufficient to spanthe height of the recess 32 and extend at least partially into the slot33 when the femoral component and intermediate component are inarticulating contact. The spine 57 serves to limit the AP movement ofthe femoral component 12. In addition, a close running fit between thespine 57 and the recess 32 helps ensure that the femoral component 12does not rotate relative to the intermediate component 16, even when thetibial component rotates relative to the intermediate component.

[0033] As shown in FIGS. 1-3 and 5, the joint prosthesis also includes alocking member 20 that closes the posterior opening 49 of the channel47. Thus, the locking member 20 retains the stabilizing post 18 withinthe channel 47. The locking member includes locking edges 69 on oppositesides of the member that are configured for locking engagement withinthe grooves 53 at the posterior end of the channel 47. The locking edges69 and grooves 53 can be configured to achieve a variety of lockingengagements therebetween to essentially permanently connect the twoparts together and close the posterior opening of the channel. Thus, inone embodiment, the locking edges and grooves can form a press-fitengagement. In a specific embodiment, the press-fit engagement can beaccomplished by complementary Morse taper angles. In another embodiment,the locking edges and grooves can be configured for a snap-fitengagement, sock as a locking tab and notch configuration. In yetanother alternative, an independent fixation, such as a screw of evenepoxy, can be used to lock the locking member 20 within the end of thechannel.

[0034] The locking member 20 operates to trap the stabilizing post 18within the channel. Thus, the member includes a stop surface 71 facingthe posterior end 65 of the post 18. The stabilizing post also includesan opposite anterior end 63 that contacts the closed end 51 of thechannel 47. The stabilizing post can thus move along the length of thechannel from an anterior position 18′ to a posterior position 18″, asdepicted in FIG. 5.

[0035] The spine 57 of the stabilizing post 18 includes an anterior face59 and an opposite posterior face 61. Each face exhibits a pre-definedcurvature for cammed movement of the stabilizing post duringarticulation of the femoral component 12 on the intermediate component16. In order to achieve this cammed movement, the femoral component, andmore particularly the intercondylar recess 32, defines aposterior-facing cam surface 77 at one end of the recess and ananterior-facing cam surface 79 at the opposite end of the recess, asshown best in FIG. 6. In essence, the two cam surfaces 77, 79 extendfrom the posterior and anterior ends of the slot 33 (FIG. 1). These camsurfaces bear against a corresponding face 59, 61 of the spine 57 tourge the stabilizing post 18 along the channel in the AP direction. Thisfeature allows the femoral component 12 to both roll and slide relativeto the tibial component without exposing the articulating components andsurfaces to the soft tissue surrounding the joint.

[0036] This rolling and sliding movement can be appreciated from acomparison of FIGS. 7 and 8. In FIG. 7, the stabilizing post 18 is inits anterior position 18′ and the femur and femoral component 12 isessential at its zero degree angle relative to the tibia and tibialcomponent 14. The posterior-facing cam surface 77 bears against theanterior face 59 of the spine 57. As the femoral component 12 begins toroll in the direction of the arrow R (FIG. 7), the cam surface 77 bearsagainst the anterior face 59 of the spine 57 to push the stabilizingpost 18 posteriorly. Eventually, the post is pushed to its posteriorposition 18″, as shown in FIG. 8. The slope and curvature of theanterior face 59 dictates the degree and speed of travel of the postalong the channel 47.

[0037] Once the stabilizing post is in its posterior position 18″, thecamming surface 77 no longer contacts the spine 57 as the femoralcomponent continues to roll and translation anteriorly relative to thetibial component. Eventually, the femoral component is in the relativeposition shown in FIG. 8 in which the femur is at an angle of about 120°relative to the tibia. The tab 34 engages the posterior indentation 73in the locking member 20 to prevent further relative rolling andtranslation (in conjunction with tension in the collateral ligaments).In this position, the anterior-facing cam surface 79 contacts theposterior face 61 of the spine 57.

[0038] As the femoral component undergoes relative rolling in theopposite direction, as designated by the arrow R′ in FIG. 8, the camsurface 79 bears against the posterior face 61 to push the spine 57anteriorly along the channel. When the cam surface 79 breaks contactwith the spine, the stabilizing post is in its relative anteriorposition 18′ (FIG. 7). The spine thus prevents further anterior relativetranslation of the femoral component 12. Again, it can be seen that noneof the articulating surfaces or components impinge or are exposed to thesurround soft tissue, even where the femoral component moves between theextreme relative positions shown in FIGS. 7 and 8.

[0039] The sliding stabilizing post 18 of the present invention providesa significant advantage during the total knee replacement procedure. Inspecifically, the specific post can be selected during the procedure andtested to verify optimum knee movement for the particular patient. Inother words, while the post 18 shown in the present figures exhibits acertain configuration, an array of posts can be available, all withdifferent profiles. For instance, the posts can be configured to permitgreater or lesser movement within the channel 47. In addition, one orboth of the faces 59, 61 can be modified to achieve a specific cammingaction when contacted by the femoral component cam surfaces 77, 79.

[0040] Thus, in accordance with one feature of the present invention,the femoral and tibial components 12, 14 can be prepared bone surfaces.The intermediate or meniscal component 16 can be mounted to the tibialcomponent 14 with the knee in flexion. A pre-selected stabilizing post18 can be slid into the channel 47 and a temporary locking member canclose the post within the channel. The knee can then be moved with theprosthesis in situ through certain degrees of motion to determinewhether the selected post is optimum for the particular patient'sanatomy. If not, the post can be removed and replaced with a differentpost having a different profile. Once an optimum stabilizing post hasbeen found, the locking member 20 can be connected to the intermediatecomponent 16 to lock the finally selected post 18 within the channel 47.

[0041] The same process can be followed with respect to the lockingmember 20. Locking members having different lengths along the channelcan be provided to allow more or less sliding movement of thestabilizing post 18 within the channel 47. In some cases, a lockingmember can be selected that does not permit any sliding of the post 18.

[0042] While the invention has been illustrated and described in detailin the drawings and foregoing description, the same should be consideredas illustrative and not restrictive in character. It is understood thatonly the preferred embodiments have been presented and that all changes,modifications and further applications that come within the spirit ofthe invention are desired to be protected. For instance, theintermediate component 16 may be made integral with the tibial component14. In this case, the rotational degree of freedom would be eliminated.

[0043] In addition, the engagement of the stabilizing post 18 to thechannel 47 can be modified so that the both ends of the channel areclosed. For example, the channel can be provided with an enlarged topopening and the base 55 of the post 18 can be configured to fit throughthe enlarged opening and then pivot to engage the grooves 53 at the baseof the channel. Engagement of the spine 57 within the intercondylarrecess 32 will prevent pivoting of the post once it is disposed withinthe channel.

[0044] In the illustrated embodiment, the channel 47 is described asincluding one closed end 51 and an opposite open end 49. Alternatively,both ends of the channel can be open with a corresponding lockingmember, such as the locking member 20, closing each end to trap thestabilizing post 18 within the. channel. The two locking members can beselected intra-operatively to optimize and orient the translation of thestabilizing post within the channel.

What is claimed is:
 1. A joint prosthesis comprising: a first jointcomponent having a bone engaging portion, an articular surface, and arecess defined within said articular surface; a mating component havinga bone engaging portion and defining a bearing surface for slidingcontact with said articular surface of said first joint component; and astabilizing post slidably mounted to said mating component amid saidbearing surface, said post projecting from said mating component andinto said recess when said articular surface is in contact with saidbearing surface.
 2. The joint prosthesis of claim 1, wherein said matingcomponent includes: a second joint component including the bone engagingportion; and an intermediate component connected to said second jointcomponent, said intermediate component including said bearing surface.3. The joint prosthesis of claim 2, wherein: said second joint componentdefines a bore; and said intermediate component includes a pin sized tobe received within said bore.
 4. The joint prosthesis of claim 3,wherein said bore and said pin are configured to permit relativerotation therebetween when said pin is received within said bore.
 5. Thejoint prosthesis of claim 1, wherein: said mating component defines anelongated channel; and said stabilizing post includes a base configuredfor sliding engagement within said channel and a spine projecting fromsaid base through said channel and into said recess when said articularsurface is in contact with said bearing surface.
 6. The joint prosthesisof claim 5, wherein: said channel is open at one end; and said matingcomponent includes a locking member configured to close said one endwith said base of said stabilizing post disposed within said channel. 7.The joint prosthesis of claim 6, wherein said locking member isconfigured for a press-fit within said channel.
 8. The joint prosthesisof claim 6, wherein: said channel includes an enlarged groove atopposite sides of said channel, said base is configured for slidingengagement within said grooves; and said locking component is configuredfor locking engagement within said grooves.
 9. The joint prosthesis ofclaim 6, wherein said locking member is selectable from a plurality oflocking members having different lengths when disposed within saidchannel.
 10. The joint prosthesis of claim 5, wherein: said channelincludes an enlarged groove at opposite sides of said channel; and saidbase is configured for sliding engagement within said grooves with saidspine projecting through said channel.
 11. The joint prosthesis of claim10, wherein said base has a length and said channel has a length greaterthan the length of said base.
 12. The joint prosthesis of claim 1,wherein said stabilizing post is selectable from a plurality ofstabilizing posts having different profiles.
 13. The joint prosthesis ofclaim 1, wherein: said recess includes surfaces at its opposite ends;said stabilizing post includes a face opposing one of said opposite endsurfaces; and said face and said one of said opposite end surfaces areconfigured to provide a camming movement of said stabilizing post assaid one of said opposite end surfaces moves in contact with said face.14. The joint prosthesis of claim 13, wherein: said stabilizing postincludes an opposite face opposing the other of said opposite endsurfaces; and said opposite face and the other of said opposite endsurfaces are configured to provide a camming movement of saidstabilizing post as said other of said opposite end surfaces moves incontact with said opposite face.
 15. The joint prosthesis of claim 14,wherein said face and said opposite face are differently curved.
 16. Ina prosthetic knee joint having a femoral component with femur engagingportion, an articular surface and a recess within the articular surface,and a tibial component with a tibia engaging portion and a bore, ameniscal component comprising: a rotation pin configured for rotatablemounting within the bore of the tibial component; a bearing surface forsliding contact with the articular surface of the femoral component; anelongated channel defined amid said bearing surface; and a stabilizingpost including a base slidably mounted with said elongated channel and aspine post projecting from said base through said channel and into therecess when the articular surface is in contact with said bearingsurface.
 17. The meniscal component of claim 16, wherein: said channelhas an open end; and said meniscal component further comprises a lockingmember configured for locking engagement at said open end of saidchannel to trap said stabilizing post within said channel.
 18. A methodfor fitting a prosthetic joint to a patient comprising the steps of:engaging a first component to a first bone of the patient, the firstcomponent having an articular surface and a recess defined within saidarticular surface; engaging a mating component to a second bone of thepatient, the mating defining a bearing surface for sliding contact withthe articular surface of the first component; selecting one of aplurality of stabilizing posts; slidably mounting the selectedstabilizing post to the mating component amid the bearing surface withthe post projecting from the mating component and into the recess whenthe articular surface is in contact with the bearing surface; evaluatingthe movement of the prosthetic joint in situ; and replacing the selectedstabilizing post with another stabilizing post from the plurality ofposts to optimize the movement of the joint.
 19. The method of claim 18,wherein: the mating component defines a channel having an open end; andthe method further comprises the step of closing the open end when astabilizing post has been selected to optimize the movement of thejoint.
 20. The method of claim 18, wherein: the mating componentincludes a second component and an intermediate component; and the stepof engaging a mating component includes engaging the second component tothe second bone and rotatably mounting the intermediate component to thesecond component.